Influence of the Pendant Arm, Halide, and Solvent on High-Efficient-Tuning [1 + 1] and [2 + 2] Schiff-Base Macrocyclic Complexes via a Zinc-Ion Template

A series of pendant-armed Schiff-base macrocyclic complexes 1–7 have been prepared by the condensation between extended dialdehydes with pendant arms (H2hpdd/H2pdd) and 1,3-propanediamine in the presence of ZnX2 (X = Cl, Br, I), where 18-membered [1 + 1] mononuclear and 36-membered [2 + 2] half-fold trinuclear macrocyclic zinc(II) complexes are yielded. Three experimental variables, i.e., the pendant arm, halide, and solvent, are found to influence the organization of final macrocyclic complexes, in addition to the conventional metal-ion template effect promoting reversible formation and cleavage of Schiff-base imine bonds. It is noted that all of the reactions produce singular macrocyclic complexes in high yields if the experimental variables are fixed, and the selection of different pendant arms and halide counterions will generate different [1 + 1] mononuclear and [2 + 2] trinuclear macrocyclic zinc(II) complexes. More interestingly, [1 + 1] and [2 + 2] macrocyclic zinc(II) complexes 2 and 3 can be produced in methanol and ethanol, respectively, in the case of the reaction between ZnBr2, H2pdd, and 1,3-propanediamine. Further experiments reveal that red solid 2 and yellow-green solid 3 can be transformed to each other just by altering the type of solvent, and this tuning is complete and reversible.